An electrical drive system comprises typically an electrical machine for driving an actuator and a converter for controlling the electrical machine. The actuator can be for example a wheel or a chain track of a mobile machine or a tool of an immobile machine. The converter can be for example a frequency converter. In many cases, an electrical drive system comprises a resolver for detecting the rotational position of the rotor of the electrical machine and the converter is configured to control the operation of the electrical machine at least partly on the basis of the detected rotational position of the rotor. The resolver can be for example a variable reluctance “VR” resolver which receives an alternative excitation signal and produces first and second alternative signals whose amplitudes are dependent on the rotational position of the resolver so that envelopes of the first and second alternative signals have a mutual phase shift. A variable reluctance resolver is advantageous in the respect that there is no need for windings in the rotor of the resolver. It is, however, also possible that the resolver is a wound-rotor resolver that comprises brushes or a rotary transformer for transferring an excitation signal to the rotor winding of the resolver. The converter is configured to transmit the excitation signal to the resolver and to receive the above-mentioned first and second alternative signals from the resolver and to generate a position signal indicative of the rotational position on the basis of the amplitudes of the first and second alternative signals and the polarity of the excitation signal.
In many electrical drive systems, an electrical machine is a multi-winding machine that comprises two or more winding systems each of which is supplied with a separate converter. The electrical machine may comprise for example two three-phase stator windings so that there is an angle of 30 electrical degrees between the respective magnetic axes of the two three-phase stator windings. In this case, each of the converters needs information indicative of the rotational position of the rotor of the electrical machine. Typically, a converter such as e.g. a frequency converter comprises a signal transfer interface for transmitting the excitation signal to a resolver and for receiving the above-mentioned first and second alternative signals from the resolver. A straightforward approach is to use as many resolvers as there are converters but it would be more cost effective to use a single resolver for all the converters. Furthermore, from the viewpoint of the product portfolio management, mutually similar converters should be capable of being used for the different winding systems of the electrical machine.
Publication US2013262009 describes a position detection device that comprises a demodulation section for receiving modulated wave signals obtained by position dependent modulation of an alternating current excitation signal and for generating position information based on the modulated wave signals by using a plurality of sampling values of the modulated wave signals. The demodulation section comprises: a) an alternating current excitation signal sampling section configured to sample the alternating current excitation signal, b) a detection section configured to receive an output of the alternating current excitation signal sampling section and execute an eliminating process of eliminating an influence caused by the sign of the alternating current excitation signal from the position information when the position information is generated based on the modulated wave signals, and c) an avoidance section configured to avoid using the alternating current excitation signal in the generation of the position information when the absolute value of the alternating current excitation signal is at most a regulated value. Publication EP1942315 describes a short-circuit detection circuit for detecting a short circuit of a signal line connected to a resolver where an excitation signal is supplied to an exciter coil and two detection signals of sine-phase and cosine-phase are electromagnetically induced in two detection coils. The short-circuit detection circuit comprises an excitation-line malfunction detection circuit for a) comparing potentials at both ends of the exciter coil to which the excitation signal is supplied by a push-pull method, b) for detecting a short circuit to the ground and/or a short circuit to the power supply based on a duty cycle of a rectangular-wave indicating a result of the comparison of the potentials at both ends of the exciter coil, and c) for outputting an excitation-line malfunction detection signal indicating a result of the detection of the short circuit.